/**
 * @author Rich Tibbett / https://github.com/richtr
 * @author mrdoob / http://mrdoob.com/
 * @author Tony Parisi / http://www.tonyparisi.com/
 * @author Takahiro / https://github.com/takahirox
 * @author Don McCurdy / https://www.donmccurdy.com
 * @author Mark Callow / https://github.com/MarkCallow
 */

/**
 * A modified version of THREE.GLTFLoader, with support for the under-development
 * KHR_texture_basisu glTF extension.
 */
THREE.GLTFLoader = ( function () {

    function GLTFLoader( manager ) {

        this.manager = ( manager !== undefined ) ? manager : THREE.DefaultLoadingManager;
        this.dracoLoader = null;
        this.ddsLoader = null;

    }

    GLTFLoader.prototype = {

        constructor: GLTFLoader,

        crossOrigin: 'anonymous',

        load: function ( url, onLoad, onProgress, onError ) {

            var scope = this;

            var resourcePath;

            if ( this.resourcePath !== undefined ) {

                resourcePath = this.resourcePath;

            } else if ( this.path !== undefined ) {

                resourcePath = this.path;

            } else {

                resourcePath = THREE.LoaderUtils.extractUrlBase( url );

            }

            // Tells the LoadingManager to track an extra item, which resolves after
            // the model is fully loaded. This means the count of items loaded will
            // be incorrect, but ensures manager.onLoad() does not fire early.
            scope.manager.itemStart( url );

            var _onError = function ( e ) {

                if ( onError ) {

                    onError( e );

                } else {

                    console.error( e );

                }

                scope.manager.itemError( url );
                scope.manager.itemEnd( url );

            };

            var loader = new THREE.FileLoader( scope.manager );

            loader.setPath( this.path );
            loader.setResponseType( 'arraybuffer' );

            if ( scope.crossOrigin === 'use-credentials' ) {

                loader.setWithCredentials( true );

            }

            loader.load( url, function ( data ) {

                try {

                    scope.parse( data, resourcePath, function ( gltf ) {

                        onLoad( gltf );

                        scope.manager.itemEnd( url );

                    }, _onError );

                } catch ( e ) {

                    _onError( e );

                }

            }, onProgress, _onError );

        },

        setCrossOrigin: function ( value ) {

            this.crossOrigin = value;
            return this;

        },

        setPath: function ( value ) {

            this.path = value;
            return this;

        },

        setResourcePath: function ( value ) {

            this.resourcePath = value;
            return this;

        },

        setDRACOLoader: function ( dracoLoader ) {

            this.dracoLoader = dracoLoader;
            return this;

        },

        setDDSLoader: function ( ddsLoader ) {

            this.ddsLoader = ddsLoader;
            return this;

        },

        parse: function ( data, path, onLoad, onError ) {

            var content;
            var extensions = {};

            if ( typeof data === 'string' ) {

                content = data;

            } else {

                var magic = THREE.LoaderUtils.decodeText( new Uint8Array( data, 0, 4 ) );

                if ( magic === BINARY_EXTENSION_HEADER_MAGIC ) {

                    try {

                        extensions[ EXTENSIONS.KHR_BINARY_GLTF ] = new GLTFBinaryExtension( data );

                    } catch ( error ) {

                        if ( onError ) onError( error );
                        return;

                    }

                    content = extensions[ EXTENSIONS.KHR_BINARY_GLTF ].content;

                } else {

                    content = THREE.LoaderUtils.decodeText( new Uint8Array( data ) );

                }

            }

            var json = JSON.parse( content );

            if ( json.asset === undefined || json.asset.version[ 0 ] < 2 ) {

                if ( onError ) onError( new Error( 'THREE.GLTFLoader: Unsupported asset. glTF versions >=2.0 are supported. Use LegacyGLTFLoader instead.' ) );
                return;

            }

            if ( json.extensionsUsed ) {

                for ( var i = 0; i < json.extensionsUsed.length; ++ i ) {

                    var extensionName = json.extensionsUsed[ i ];
                    var extensionsRequired = json.extensionsRequired || [];

                    switch ( extensionName ) {

                        case EXTENSIONS.KHR_LIGHTS_PUNCTUAL:
                            extensions[ extensionName ] = new GLTFLightsExtension( json );
                            break;

                        case EXTENSIONS.KHR_MATERIALS_UNLIT:
                            extensions[ extensionName ] = new GLTFMaterialsUnlitExtension();
                            break;

                        case EXTENSIONS.KHR_MATERIALS_PBR_SPECULAR_GLOSSINESS:
                            extensions[ extensionName ] = new GLTFMaterialsPbrSpecularGlossinessExtension();
                            break;

                        case EXTENSIONS.KHR_DRACO_MESH_COMPRESSION:
                            extensions[ extensionName ] = new GLTFDracoMeshCompressionExtension( json, this.dracoLoader );
                            break;

                        case EXTENSIONS.MSFT_TEXTURE_DDS:
                            extensions[ EXTENSIONS.MSFT_TEXTURE_DDS ] = new GLTFTextureDDSExtension( this.ddsLoader );
                            break;

                        case EXTENSIONS.KHR_TEXTURE_BASISU:
                            extensions[ EXTENSIONS.KHR_TEXTURE_BASISU ] = new GLTFTextureBasisuExtension();
                            break;

                        case EXTENSIONS.KHR_TEXTURE_TRANSFORM:
                            extensions[ EXTENSIONS.KHR_TEXTURE_TRANSFORM ] = new GLTFTextureTransformExtension();
                            break;

                        default:

                            if ( extensionsRequired.indexOf( extensionName ) >= 0 ) {

                                console.warn( 'THREE.GLTFLoader: Unknown extension "' + extensionName + '".' );

                            }

                    }

                }

            }

            var parser = new GLTFParser( json, extensions, {

                path: path || this.resourcePath || '',
                crossOrigin: this.crossOrigin,
                manager: this.manager

            } );

            parser.parse( onLoad, onError );

        }

    };

    /* GLTFREGISTRY */

    function GLTFRegistry() {

        var objects = {};

        return  {

            get: function ( key ) {

                return objects[ key ];

            },

            add: function ( key, object ) {

                objects[ key ] = object;

            },

            remove: function ( key ) {

                delete objects[ key ];

            },

            removeAll: function () {

                objects = {};

            }

        };

    }

    /*********************************/
    /********** EXTENSIONS ***********/
    /*********************************/

    var EXTENSIONS = {
        KHR_BINARY_GLTF: 'KHR_binary_glTF',
        KHR_DRACO_MESH_COMPRESSION: 'KHR_draco_mesh_compression',
        KHR_LIGHTS_PUNCTUAL: 'KHR_lights_punctual',
        KHR_MATERIALS_PBR_SPECULAR_GLOSSINESS: 'KHR_materials_pbrSpecularGlossiness',
        KHR_MATERIALS_UNLIT: 'KHR_materials_unlit',
        KHR_TEXTURE_TRANSFORM: 'KHR_texture_transform',
        MSFT_TEXTURE_DDS: 'MSFT_texture_dds',
        KHR_TEXTURE_BASISU: 'KHR_texture_basisu'
    };

    /**
     * DDS Texture Extension
     *
     * Specification:
     * https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Vendor/MSFT_texture_dds
     *
     */
    function GLTFTextureDDSExtension( ddsLoader ) {

        if ( ! ddsLoader ) {

            throw new Error( 'THREE.GLTFLoader: Attempting to load .dds texture without importing THREE.DDSLoader' );

        }

        this.name = EXTENSIONS.MSFT_TEXTURE_DDS;
        this.ddsLoader = ddsLoader;

    }

   /**
    * Basis Texture Extension
    */
  function GLTFTextureBasisuExtension() {

    this.name = EXTENSIONS.KHR_TEXTURE_BASISU;

  }

    /**
     * Lights Extension
     *
     * Specification: PENDING
     */
    function GLTFLightsExtension( json ) {

        this.name = EXTENSIONS.KHR_LIGHTS_PUNCTUAL;

        var extension = ( json.extensions && json.extensions[ EXTENSIONS.KHR_LIGHTS_PUNCTUAL ] ) || {};
        this.lightDefs = extension.lights || [];

    }

    GLTFLightsExtension.prototype.loadLight = function ( lightIndex ) {

        var lightDef = this.lightDefs[ lightIndex ];
        var lightNode;

        var color = new THREE.Color( 0xffffff );
        if ( lightDef.color !== undefined ) color.fromArray( lightDef.color );

        var range = lightDef.range !== undefined ? lightDef.range : 0;

        switch ( lightDef.type ) {

            case 'directional':
                lightNode = new THREE.DirectionalLight( color );
                lightNode.target.position.set( 0, 0, - 1 );
                lightNode.add( lightNode.target );
                break;

            case 'point':
                lightNode = new THREE.PointLight( color );
                lightNode.distance = range;
                break;

            case 'spot':
                lightNode = new THREE.SpotLight( color );
                lightNode.distance = range;
                // Handle spotlight properties.
                lightDef.spot = lightDef.spot || {};
                lightDef.spot.innerConeAngle = lightDef.spot.innerConeAngle !== undefined ? lightDef.spot.innerConeAngle : 0;
                lightDef.spot.outerConeAngle = lightDef.spot.outerConeAngle !== undefined ? lightDef.spot.outerConeAngle : Math.PI / 4.0;
                lightNode.angle = lightDef.spot.outerConeAngle;
                lightNode.penumbra = 1.0 - lightDef.spot.innerConeAngle / lightDef.spot.outerConeAngle;
                lightNode.target.position.set( 0, 0, - 1 );
                lightNode.add( lightNode.target );
                break;

            default:
                throw new Error( 'THREE.GLTFLoader: Unexpected light type, "' + lightDef.type + '".' );

        }

        // Some lights (e.g. spot) default to a position other than the origin. Reset the position
        // here, because node-level parsing will only override position if explicitly specified.
        lightNode.position.set( 0, 0, 0 );

        lightNode.decay = 2;

        if ( lightDef.intensity !== undefined ) lightNode.intensity = lightDef.intensity;

        lightNode.name = lightDef.name || ( 'light_' + lightIndex );

        return Promise.resolve( lightNode );

    };

    /**
     * Unlit Materials Extension (pending)
     *
     * PR: https://github.com/KhronosGroup/glTF/pull/1163
     */
    function GLTFMaterialsUnlitExtension() {

        this.name = EXTENSIONS.KHR_MATERIALS_UNLIT;

    }

    GLTFMaterialsUnlitExtension.prototype.getMaterialType = function () {

        return THREE.MeshBasicMaterial;

    };

    GLTFMaterialsUnlitExtension.prototype.extendParams = function ( materialParams, materialDef, parser ) {

        var pending = [];

        materialParams.color = new THREE.Color( 1.0, 1.0, 1.0 );
        materialParams.opacity = 1.0;

        var metallicRoughness = materialDef.pbrMetallicRoughness;

        if ( metallicRoughness ) {

            if ( Array.isArray( metallicRoughness.baseColorFactor ) ) {

                var array = metallicRoughness.baseColorFactor;

                materialParams.color.fromArray( array );
                materialParams.opacity = array[ 3 ];

            }

            if ( metallicRoughness.baseColorTexture !== undefined ) {

                pending.push( parser.assignTexture( materialParams, 'map', metallicRoughness.baseColorTexture ) );

            }

        }

        return Promise.all( pending );

    };

    /* BINARY EXTENSION */
    var BINARY_EXTENSION_HEADER_MAGIC = 'glTF';
    var BINARY_EXTENSION_HEADER_LENGTH = 12;
    var BINARY_EXTENSION_CHUNK_TYPES = { JSON: 0x4E4F534A, BIN: 0x004E4942 };

    function GLTFBinaryExtension( data ) {

        this.name = EXTENSIONS.KHR_BINARY_GLTF;
        this.content = null;
        this.body = null;

        var headerView = new DataView( data, 0, BINARY_EXTENSION_HEADER_LENGTH );

        this.header = {
            magic: THREE.LoaderUtils.decodeText( new Uint8Array( data.slice( 0, 4 ) ) ),
            version: headerView.getUint32( 4, true ),
            length: headerView.getUint32( 8, true )
        };

        if ( this.header.magic !== BINARY_EXTENSION_HEADER_MAGIC ) {

            throw new Error( 'THREE.GLTFLoader: Unsupported glTF-Binary header.' );

        } else if ( this.header.version < 2.0 ) {

            throw new Error( 'THREE.GLTFLoader: Legacy binary file detected. Use LegacyGLTFLoader instead.' );

        }

        var chunkView = new DataView( data, BINARY_EXTENSION_HEADER_LENGTH );
        var chunkIndex = 0;

        while ( chunkIndex < chunkView.byteLength ) {

            var chunkLength = chunkView.getUint32( chunkIndex, true );
            chunkIndex += 4;

            var chunkType = chunkView.getUint32( chunkIndex, true );
            chunkIndex += 4;

            if ( chunkType === BINARY_EXTENSION_CHUNK_TYPES.JSON ) {

                var contentArray = new Uint8Array( data, BINARY_EXTENSION_HEADER_LENGTH + chunkIndex, chunkLength );
                this.content = THREE.LoaderUtils.decodeText( contentArray );

            } else if ( chunkType === BINARY_EXTENSION_CHUNK_TYPES.BIN ) {

                var byteOffset = BINARY_EXTENSION_HEADER_LENGTH + chunkIndex;
                this.body = data.slice( byteOffset, byteOffset + chunkLength );

            }

            // Clients must ignore chunks with unknown types.

            chunkIndex += chunkLength;

        }

        if ( this.content === null ) {

            throw new Error( 'THREE.GLTFLoader: JSON content not found.' );

        }

    }

    /**
     * DRACO Mesh Compression Extension
     *
     * Specification: https://github.com/KhronosGroup/glTF/pull/874
     */
    function GLTFDracoMeshCompressionExtension( json, dracoLoader ) {

        if ( ! dracoLoader ) {

            throw new Error( 'THREE.GLTFLoader: No DRACOLoader instance provided.' );

        }

        this.name = EXTENSIONS.KHR_DRACO_MESH_COMPRESSION;
        this.json = json;
        this.dracoLoader = dracoLoader;

    }

    GLTFDracoMeshCompressionExtension.prototype.decodePrimitive = function ( primitive, parser ) {

        var json = this.json;
        var dracoLoader = this.dracoLoader;
        var bufferViewIndex = primitive.extensions[ this.name ].bufferView;
        var gltfAttributeMap = primitive.extensions[ this.name ].attributes;
        var threeAttributeMap = {};
        var attributeNormalizedMap = {};
        var attributeTypeMap = {};

        for ( var attributeName in gltfAttributeMap ) {

            var threeAttributeName = ATTRIBUTES[ attributeName ] || attributeName.toLowerCase();

            threeAttributeMap[ threeAttributeName ] = gltfAttributeMap[ attributeName ];

        }

        for ( attributeName in primitive.attributes ) {

            var threeAttributeName = ATTRIBUTES[ attributeName ] || attributeName.toLowerCase();

            if ( gltfAttributeMap[ attributeName ] !== undefined ) {

                var accessorDef = json.accessors[ primitive.attributes[ attributeName ] ];
                var componentType = WEBGL_COMPONENT_TYPES[ accessorDef.componentType ];

                attributeTypeMap[ threeAttributeName ] = componentType;
                attributeNormalizedMap[ threeAttributeName ] = accessorDef.normalized === true;

            }

        }

        return parser.getDependency( 'bufferView', bufferViewIndex ).then( function ( bufferView ) {

            return new Promise( function ( resolve ) {

                dracoLoader.decodeDracoFile( bufferView, function ( geometry ) {

                    for ( var attributeName in geometry.attributes ) {

                        var attribute = geometry.attributes[ attributeName ];
                        var normalized = attributeNormalizedMap[ attributeName ];

                        if ( normalized !== undefined ) attribute.normalized = normalized;

                    }

                    resolve( geometry );

                }, threeAttributeMap, attributeTypeMap );

            } );

        } );

    };

    /**
     * Texture Transform Extension
     *
     * Specification:
     */
    function GLTFTextureTransformExtension() {

        this.name = EXTENSIONS.KHR_TEXTURE_TRANSFORM;

    }

    GLTFTextureTransformExtension.prototype.extendTexture = function ( texture, transform ) {

        texture = texture.clone();

        if ( transform.offset !== undefined ) {

            texture.offset.fromArray( transform.offset );

        }

        if ( transform.rotation !== undefined ) {

            texture.rotation = transform.rotation;

        }

        if ( transform.scale !== undefined ) {

            texture.repeat.fromArray( transform.scale );

        }

        if ( transform.texCoord !== undefined ) {

            console.warn( 'THREE.GLTFLoader: Custom UV sets in "' + this.name + '" extension not yet supported.' );

        }

        texture.needsUpdate = true;

        return texture;

    };

    /**
     * Specular-Glossiness Extension
     *
     * Specification: https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_materials_pbrSpecularGlossiness
     */
    function GLTFMaterialsPbrSpecularGlossinessExtension() {

        return {

            name: EXTENSIONS.KHR_MATERIALS_PBR_SPECULAR_GLOSSINESS,

            specularGlossinessParams: [
                'color',
                'map',
                'lightMap',
                'lightMapIntensity',
                'aoMap',
                'aoMapIntensity',
                'emissive',
                'emissiveIntensity',
                'emissiveMap',
                'bumpMap',
                'bumpScale',
                'normalMap',
                'displacementMap',
                'displacementScale',
                'displacementBias',
                'specularMap',
                'specular',
                'glossinessMap',
                'glossiness',
                'alphaMap',
                'envMap',
                'envMapIntensity',
                'refractionRatio',
            ],

            getMaterialType: function () {

                return THREE.ShaderMaterial;

            },

            extendParams: function ( materialParams, materialDef, parser ) {

                var pbrSpecularGlossiness = materialDef.extensions[ this.name ];

                var shader = THREE.ShaderLib[ 'standard' ];

                var uniforms = THREE.UniformsUtils.clone( shader.uniforms );

                var specularMapParsFragmentChunk = [
                    '#ifdef USE_SPECULARMAP',
                    '   uniform sampler2D specularMap;',
                    '#endif'
                ].join( '\n' );

                var glossinessMapParsFragmentChunk = [
                    '#ifdef USE_GLOSSINESSMAP',
                    '   uniform sampler2D glossinessMap;',
                    '#endif'
                ].join( '\n' );

                var specularMapFragmentChunk = [
                    'vec3 specularFactor = specular;',
                    '#ifdef USE_SPECULARMAP',
                    '   vec4 texelSpecular = texture2D( specularMap, vUv );',
                    '   texelSpecular = sRGBToLinear( texelSpecular );',
                    '   // reads channel RGB, compatible with a glTF Specular-Glossiness (RGBA) texture',
                    '   specularFactor *= texelSpecular.rgb;',
                    '#endif'
                ].join( '\n' );

                var glossinessMapFragmentChunk = [
                    'float glossinessFactor = glossiness;',
                    '#ifdef USE_GLOSSINESSMAP',
                    '   vec4 texelGlossiness = texture2D( glossinessMap, vUv );',
                    '   // reads channel A, compatible with a glTF Specular-Glossiness (RGBA) texture',
                    '   glossinessFactor *= texelGlossiness.a;',
                    '#endif'
                ].join( '\n' );

                var lightPhysicalFragmentChunk = [
                    'PhysicalMaterial material;',
                    'material.diffuseColor = diffuseColor.rgb;',
                    'material.specularRoughness = clamp( 1.0 - glossinessFactor, 0.04, 1.0 );',
                    'material.specularColor = specularFactor.rgb;',
                ].join( '\n' );

                var fragmentShader = shader.fragmentShader
                    .replace( 'uniform float roughness;', 'uniform vec3 specular;' )
                    .replace( 'uniform float metalness;', 'uniform float glossiness;' )
                    .replace( '#include <roughnessmap_pars_fragment>', specularMapParsFragmentChunk )
                    .replace( '#include <metalnessmap_pars_fragment>', glossinessMapParsFragmentChunk )
                    .replace( '#include <roughnessmap_fragment>', specularMapFragmentChunk )
                    .replace( '#include <metalnessmap_fragment>', glossinessMapFragmentChunk )
                    .replace( '#include <lights_physical_fragment>', lightPhysicalFragmentChunk );

                delete uniforms.roughness;
                delete uniforms.metalness;
                delete uniforms.roughnessMap;
                delete uniforms.metalnessMap;

                uniforms.specular = { value: new THREE.Color().setHex( 0x111111 ) };
                uniforms.glossiness = { value: 0.5 };
                uniforms.specularMap = { value: null };
                uniforms.glossinessMap = { value: null };

                materialParams.vertexShader = shader.vertexShader;
                materialParams.fragmentShader = fragmentShader;
                materialParams.uniforms = uniforms;
                materialParams.defines = { 'STANDARD': '' }

                materialParams.color = new THREE.Color( 1.0, 1.0, 1.0 );
                materialParams.opacity = 1.0;

                var pending = [];

                if ( Array.isArray( pbrSpecularGlossiness.diffuseFactor ) ) {

                    var array = pbrSpecularGlossiness.diffuseFactor;

                    materialParams.color.fromArray( array );
                    materialParams.opacity = array[ 3 ];

                }

                if ( pbrSpecularGlossiness.diffuseTexture !== undefined ) {

                    pending.push( parser.assignTexture( materialParams, 'map', pbrSpecularGlossiness.diffuseTexture ) );

                }

                materialParams.emissive = new THREE.Color( 0.0, 0.0, 0.0 );
                materialParams.glossiness = pbrSpecularGlossiness.glossinessFactor !== undefined ? pbrSpecularGlossiness.glossinessFactor : 1.0;
                materialParams.specular = new THREE.Color( 1.0, 1.0, 1.0 );

                if ( Array.isArray( pbrSpecularGlossiness.specularFactor ) ) {

                    materialParams.specular.fromArray( pbrSpecularGlossiness.specularFactor );

                }

                if ( pbrSpecularGlossiness.specularGlossinessTexture !== undefined ) {

                    var specGlossMapDef = pbrSpecularGlossiness.specularGlossinessTexture;
                    pending.push( parser.assignTexture( materialParams, 'glossinessMap', specGlossMapDef ) );
                    pending.push( parser.assignTexture( materialParams, 'specularMap', specGlossMapDef ) );

                }

                return Promise.all( pending );

            },

            createMaterial: function ( params ) {

                // setup material properties based on MeshStandardMaterial for Specular-Glossiness

                var material = new THREE.ShaderMaterial( {
                    defines: params.defines,
                    vertexShader: params.vertexShader,
                    fragmentShader: params.fragmentShader,
                    uniforms: params.uniforms,
                    fog: true,
                    lights: true,
                    opacity: params.opacity,
                    transparent: params.transparent
                } );

                material.isGLTFSpecularGlossinessMaterial = true;

                material.color = params.color;

                material.map = params.map === undefined ? null : params.map;

                material.lightMap = null;
                material.lightMapIntensity = 1.0;

                material.aoMap = params.aoMap === undefined ? null : params.aoMap;
                material.aoMapIntensity = 1.0;

                material.emissive = params.emissive;
                material.emissiveIntensity = 1.0;
                material.emissiveMap = params.emissiveMap === undefined ? null : params.emissiveMap;

                material.bumpMap = params.bumpMap === undefined ? null : params.bumpMap;
                material.bumpScale = 1;

                material.normalMap = params.normalMap === undefined ? null : params.normalMap;

                if ( params.normalScale ) material.normalScale = params.normalScale;

                material.displacementMap = null;
                material.displacementScale = 1;
                material.displacementBias = 0;

                material.specularMap = params.specularMap === undefined ? null : params.specularMap;
                material.specular = params.specular;

                material.glossinessMap = params.glossinessMap === undefined ? null : params.glossinessMap;
                material.glossiness = params.glossiness;

                material.alphaMap = null;

                material.envMap = params.envMap === undefined ? null : params.envMap;
                material.envMapIntensity = 1.0;

                material.refractionRatio = 0.98;

                material.extensions.derivatives = true;

                return material;

            },

            /**
             * Clones a GLTFSpecularGlossinessMaterial instance. The ShaderMaterial.copy() method can
             * copy only properties it knows about or inherits, and misses many properties that would
             * normally be defined by MeshStandardMaterial.
             *
             * This method allows GLTFSpecularGlossinessMaterials to be cloned in the process of
             * loading a glTF model, but cloning later (e.g. by the user) would require these changes
             * AND also updating `.onBeforeRender` on the parent mesh.
             *
             * @param  {THREE.ShaderMaterial} source
             * @return {THREE.ShaderMaterial}
             */
            cloneMaterial: function ( source ) {

                var target = source.clone();

                target.isGLTFSpecularGlossinessMaterial = true;

                var params = this.specularGlossinessParams;

                for ( var i = 0, il = params.length; i < il; i ++ ) {

                    var value = source[ params[ i ] ];
                    target[ params[ i ] ] = ( value && value.isColor ) ? value.clone() : value;

                }

                return target;

            },

            // Here's based on refreshUniformsCommon() and refreshUniformsStandard() in WebGLRenderer.
            refreshUniforms: function ( renderer, scene, camera, geometry, material ) {

                if ( material.isGLTFSpecularGlossinessMaterial !== true ) {

                    return;

                }

                var uniforms = material.uniforms;
                var defines = material.defines;

                uniforms.opacity.value = material.opacity;

                uniforms.diffuse.value.copy( material.color );
                uniforms.emissive.value.copy( material.emissive ).multiplyScalar( material.emissiveIntensity );

                uniforms.map.value = material.map;
                uniforms.specularMap.value = material.specularMap;
                uniforms.alphaMap.value = material.alphaMap;

                uniforms.lightMap.value = material.lightMap;
                uniforms.lightMapIntensity.value = material.lightMapIntensity;

                uniforms.aoMap.value = material.aoMap;
                uniforms.aoMapIntensity.value = material.aoMapIntensity;

                // uv repeat and offset setting priorities
                // 1. color map
                // 2. specular map
                // 3. normal map
                // 4. bump map
                // 5. alpha map
                // 6. emissive map

                var uvScaleMap;

                if ( material.map ) {

                    uvScaleMap = material.map;

                } else if ( material.specularMap ) {

                    uvScaleMap = material.specularMap;

                } else if ( material.displacementMap ) {

                    uvScaleMap = material.displacementMap;

                } else if ( material.normalMap ) {

                    uvScaleMap = material.normalMap;

                } else if ( material.bumpMap ) {

                    uvScaleMap = material.bumpMap;

                } else if ( material.glossinessMap ) {

                    uvScaleMap = material.glossinessMap;

                } else if ( material.alphaMap ) {

                    uvScaleMap = material.alphaMap;

                } else if ( material.emissiveMap ) {

                    uvScaleMap = material.emissiveMap;

                }

                if ( uvScaleMap !== undefined ) {

                    // backwards compatibility
                    if ( uvScaleMap.isWebGLRenderTarget ) {

                        uvScaleMap = uvScaleMap.texture;

                    }

                    if ( uvScaleMap.matrixAutoUpdate === true ) {

                        uvScaleMap.updateMatrix();

                    }

                    uniforms.uvTransform.value.copy( uvScaleMap.matrix );

                }

                if ( material.envMap ) {

                    uniforms.envMap.value = material.envMap;
                    uniforms.envMapIntensity.value = material.envMapIntensity;

                    // don't flip CubeTexture envMaps, flip everything else:
                    //  WebGLRenderTargetCube will be flipped for backwards compatibility
                    //  WebGLRenderTargetCube.texture will be flipped because it's a Texture and NOT a CubeTexture
                    // this check must be handled differently, or removed entirely, if WebGLRenderTargetCube uses a CubeTexture in the future
                    uniforms.flipEnvMap.value = material.envMap.isCubeTexture ? - 1 : 1;

                    uniforms.reflectivity.value = material.reflectivity;
                    uniforms.refractionRatio.value = material.refractionRatio;

                    uniforms.maxMipLevel.value = renderer.properties.get( material.envMap ).__maxMipLevel;

                }

                uniforms.specular.value.copy( material.specular );
                uniforms.glossiness.value = material.glossiness;

                uniforms.glossinessMap.value = material.glossinessMap;

                uniforms.emissiveMap.value = material.emissiveMap;
                uniforms.bumpMap.value = material.bumpMap;
                uniforms.normalMap.value = material.normalMap;

                uniforms.displacementMap.value = material.displacementMap;
                uniforms.displacementScale.value = material.displacementScale;
                uniforms.displacementBias.value = material.displacementBias;

                if ( uniforms.glossinessMap.value !== null && defines.USE_GLOSSINESSMAP === undefined ) {

                    defines.USE_GLOSSINESSMAP = '';
                    // set USE_ROUGHNESSMAP to enable vUv
                    defines.USE_ROUGHNESSMAP = '';

                }

                if ( uniforms.glossinessMap.value === null && defines.USE_GLOSSINESSMAP !== undefined ) {

                    delete defines.USE_GLOSSINESSMAP;
                    delete defines.USE_ROUGHNESSMAP;

                }

            }

        };

    }

    /*********************************/
    /********** INTERPOLATION ********/
    /*********************************/

    // Spline Interpolation
    // Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#appendix-c-spline-interpolation
    function GLTFCubicSplineInterpolant( parameterPositions, sampleValues, sampleSize, resultBuffer ) {

        THREE.Interpolant.call( this, parameterPositions, sampleValues, sampleSize, resultBuffer );

    }

    GLTFCubicSplineInterpolant.prototype = Object.create( THREE.Interpolant.prototype );
    GLTFCubicSplineInterpolant.prototype.constructor = GLTFCubicSplineInterpolant;

    GLTFCubicSplineInterpolant.prototype.copySampleValue_ = function ( index ) {

        // Copies a sample value to the result buffer. See description of glTF
        // CUBICSPLINE values layout in interpolate_() function below.

        var result = this.resultBuffer,
            values = this.sampleValues,
            valueSize = this.valueSize,
            offset = index * valueSize * 3 + valueSize;

        for ( var i = 0; i !== valueSize; i ++ ) {

            result[ i ] = values[ offset + i ];

        }

        return result;

    };

    GLTFCubicSplineInterpolant.prototype.beforeStart_ = GLTFCubicSplineInterpolant.prototype.copySampleValue_;

    GLTFCubicSplineInterpolant.prototype.afterEnd_ = GLTFCubicSplineInterpolant.prototype.copySampleValue_;

    GLTFCubicSplineInterpolant.prototype.interpolate_ = function ( i1, t0, t, t1 ) {

        var result = this.resultBuffer;
        var values = this.sampleValues;
        var stride = this.valueSize;

        var stride2 = stride * 2;
        var stride3 = stride * 3;

        var td = t1 - t0;

        var p = ( t - t0 ) / td;
        var pp = p * p;
        var ppp = pp * p;

        var offset1 = i1 * stride3;
        var offset0 = offset1 - stride3;

        var s2 = - 2 * ppp + 3 * pp;
        var s3 = ppp - pp;
        var s0 = 1 - s2;
        var s1 = s3 - pp + p;

        // Layout of keyframe output values for CUBICSPLINE animations:
        //   [ inTangent_1, splineVertex_1, outTangent_1, inTangent_2, splineVertex_2, ... ]
        for ( var i = 0; i !== stride; i ++ ) {

            var p0 = values[ offset0 + i + stride ]; // splineVertex_k
            var m0 = values[ offset0 + i + stride2 ] * td; // outTangent_k * (t_k+1 - t_k)
            var p1 = values[ offset1 + i + stride ]; // splineVertex_k+1
            var m1 = values[ offset1 + i ] * td; // inTangent_k+1 * (t_k+1 - t_k)

            result[ i ] = s0 * p0 + s1 * m0 + s2 * p1 + s3 * m1;

        }

        return result;

    };

    /*********************************/
    /********** INTERNALS ************/
    /*********************************/

    /* CONSTANTS */

    var WEBGL_CONSTANTS = {
        FLOAT: 5126,
        //FLOAT_MAT2: 35674,
        FLOAT_MAT3: 35675,
        FLOAT_MAT4: 35676,
        FLOAT_VEC2: 35664,
        FLOAT_VEC3: 35665,
        FLOAT_VEC4: 35666,
        LINEAR: 9729,
        REPEAT: 10497,
        SAMPLER_2D: 35678,
        POINTS: 0,
        LINES: 1,
        LINE_LOOP: 2,
        LINE_STRIP: 3,
        TRIANGLES: 4,
        TRIANGLE_STRIP: 5,
        TRIANGLE_FAN: 6,
        UNSIGNED_BYTE: 5121,
        UNSIGNED_SHORT: 5123
    };

    var WEBGL_COMPONENT_TYPES = {
        5120: Int8Array,
        5121: Uint8Array,
        5122: Int16Array,
        5123: Uint16Array,
        5125: Uint32Array,
        5126: Float32Array
    };

    var WEBGL_FILTERS = {
        9728: THREE.NearestFilter,
        9729: THREE.LinearFilter,
        9984: THREE.NearestMipmapNearestFilter,
        9985: THREE.LinearMipmapNearestFilter,
        9986: THREE.NearestMipmapLinearFilter,
        9987: THREE.LinearMipmapLinearFilter
    };

    var WEBGL_WRAPPINGS = {
        33071: THREE.ClampToEdgeWrapping,
        33648: THREE.MirroredRepeatWrapping,
        10497: THREE.RepeatWrapping
    };

    var WEBGL_TYPE_SIZES = {
        'SCALAR': 1,
        'VEC2': 2,
        'VEC3': 3,
        'VEC4': 4,
        'MAT2': 4,
        'MAT3': 9,
        'MAT4': 16
    };

    var ATTRIBUTES = {
        POSITION: 'position',
        NORMAL: 'normal',
        TANGENT: 'tangent',
        TEXCOORD_0: 'uv',
        TEXCOORD_1: 'uv2',
        COLOR_0: 'color',
        WEIGHTS_0: 'skinWeight',
        JOINTS_0: 'skinIndex',
    };

    var PATH_PROPERTIES = {
        scale: 'scale',
        translation: 'position',
        rotation: 'quaternion',
        weights: 'morphTargetInfluences'
    };

    var INTERPOLATION = {
        CUBICSPLINE: undefined, // We use a custom interpolant (GLTFCubicSplineInterpolation) for CUBICSPLINE tracks. Each
                                // keyframe track will be initialized with a default interpolation type, then modified.
        LINEAR: THREE.InterpolateLinear,
        STEP: THREE.InterpolateDiscrete
    };

    var ALPHA_MODES = {
        OPAQUE: 'OPAQUE',
        MASK: 'MASK',
        BLEND: 'BLEND'
    };

    var MIME_TYPE_FORMATS = {
        'image/png': THREE.RGBAFormat,
        'image/jpeg': THREE.RGBFormat
    };

    /* UTILITY FUNCTIONS */

    function resolveURL( url, path ) {

        // Invalid URL
        if ( typeof url !== 'string' || url === '' ) return '';
        
        // Host Relative URL
        if ( /^https?:\/\//i.test( path ) && /^\//.test( url ) ) {

            path = path.replace( /(^https?:\/\/[^\/]+).*/i , '$1' );

        }

        // Absolute URL http://,https://,//
        if ( /^(https?:)?\/\//i.test( url ) ) return url;

        // Data URI
        if ( /^data:.*,.*$/i.test( url ) ) return url;

        // Blob URL
        if ( /^blob:.*$/i.test( url ) ) return url;

        // Relative URL
        return path + url;

    }

    var defaultMaterial;

    /**
     * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#default-material
     */
    function createDefaultMaterial() {

        defaultMaterial = defaultMaterial || new THREE.MeshStandardMaterial( {
            color: 0xFFFFFF,
            emissive: 0x000000,
            metalness: 1,
            roughness: 1,
            transparent: false,
            depthTest: true,
            side: THREE.FrontSide
        } );

        return defaultMaterial;

    }

    function addUnknownExtensionsToUserData( knownExtensions, object, objectDef ) {

        // Add unknown glTF extensions to an object's userData.

        for ( var name in objectDef.extensions ) {

            if ( knownExtensions[ name ] === undefined ) {

                object.userData.gltfExtensions = object.userData.gltfExtensions || {};
                object.userData.gltfExtensions[ name ] = objectDef.extensions[ name ];

            }

        }

    }

    /**
     * @param {THREE.Object3D|THREE.Material|THREE.BufferGeometry} object
     * @param {GLTF.definition} gltfDef
     */
    function assignExtrasToUserData( object, gltfDef ) {

        if ( gltfDef.extras !== undefined ) {

            if ( typeof gltfDef.extras === 'object' ) {

                Object.assign( object.userData, gltfDef.extras );

            } else {

                console.warn( 'THREE.GLTFLoader: Ignoring primitive type .extras, ' + gltfDef.extras );

            }

        }

    }

    /**
     * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#morph-targets
     *
     * @param {THREE.BufferGeometry} geometry
     * @param {Array<GLTF.Target>} targets
     * @param {GLTFParser} parser
     * @return {Promise<THREE.BufferGeometry>}
     */
    function addMorphTargets( geometry, targets, parser ) {

        var hasMorphPosition = false;
        var hasMorphNormal = false;

        for ( var i = 0, il = targets.length; i < il; i ++ ) {

            var target = targets[ i ];

            if ( target.POSITION !== undefined ) hasMorphPosition = true;
            if ( target.NORMAL !== undefined ) hasMorphNormal = true;

            if ( hasMorphPosition && hasMorphNormal ) break;

        }

        if ( ! hasMorphPosition && ! hasMorphNormal ) return Promise.resolve( geometry );

        var pendingPositionAccessors = [];
        var pendingNormalAccessors = [];

        for ( var i = 0, il = targets.length; i < il; i ++ ) {

            var target = targets[ i ];

            if ( hasMorphPosition ) {

                var pendingAccessor = target.POSITION !== undefined
                    ? parser.getDependency( 'accessor', target.POSITION )
                    : geometry.attributes.position;

                pendingPositionAccessors.push( pendingAccessor );

            }

            if ( hasMorphNormal ) {

                var pendingAccessor = target.NORMAL !== undefined
                    ? parser.getDependency( 'accessor', target.NORMAL )
                    : geometry.attributes.normal;

                pendingNormalAccessors.push( pendingAccessor );

            }

        }

        return Promise.all( [
            Promise.all( pendingPositionAccessors ),
            Promise.all( pendingNormalAccessors )
        ] ).then( function ( accessors ) {

            var morphPositions = accessors[ 0 ];
            var morphNormals = accessors[ 1 ];

            // Clone morph target accessors before modifying them.

            for ( var i = 0, il = morphPositions.length; i < il; i ++ ) {

                if ( geometry.attributes.position === morphPositions[ i ] ) continue;

                morphPositions[ i ] = cloneBufferAttribute( morphPositions[ i ] );

            }

            for ( var i = 0, il = morphNormals.length; i < il; i ++ ) {

                if ( geometry.attributes.normal === morphNormals[ i ] ) continue;

                morphNormals[ i ] = cloneBufferAttribute( morphNormals[ i ] );

            }

            for ( var i = 0, il = targets.length; i < il; i ++ ) {

                var target = targets[ i ];
                var attributeName = 'morphTarget' + i;

                if ( hasMorphPosition ) {

                    // Three.js morph position is absolute value. The formula is
                    //   basePosition
                    //     + weight0 * ( morphPosition0 - basePosition )
                    //     + weight1 * ( morphPosition1 - basePosition )
                    //     ...
                    // while the glTF one is relative
                    //   basePosition
                    //     + weight0 * glTFmorphPosition0
                    //     + weight1 * glTFmorphPosition1
                    //     ...
                    // then we need to convert from relative to absolute here.

                    if ( target.POSITION !== undefined ) {

                        var positionAttribute = morphPositions[ i ];
                        positionAttribute.name = attributeName;

                        var position = geometry.attributes.position;

                        for ( var j = 0, jl = positionAttribute.count; j < jl; j ++ ) {

                            positionAttribute.setXYZ(
                                j,
                                positionAttribute.getX( j ) + position.getX( j ),
                                positionAttribute.getY( j ) + position.getY( j ),
                                positionAttribute.getZ( j ) + position.getZ( j )
                            );

                        }

                    }

                }

                if ( hasMorphNormal ) {

                    // see target.POSITION's comment

                    if ( target.NORMAL !== undefined ) {

                        var normalAttribute = morphNormals[ i ];
                        normalAttribute.name = attributeName;

                        var normal = geometry.attributes.normal;

                        for ( var j = 0, jl = normalAttribute.count; j < jl; j ++ ) {

                            normalAttribute.setXYZ(
                                j,
                                normalAttribute.getX( j ) + normal.getX( j ),
                                normalAttribute.getY( j ) + normal.getY( j ),
                                normalAttribute.getZ( j ) + normal.getZ( j )
                            );

                        }

                    }

                }

            }

            if ( hasMorphPosition ) geometry.morphAttributes.position = morphPositions;
            if ( hasMorphNormal ) geometry.morphAttributes.normal = morphNormals;

            return geometry;

        } );

    }

    /**
     * @param {THREE.Mesh} mesh
     * @param {GLTF.Mesh} meshDef
     */
    function updateMorphTargets( mesh, meshDef ) {

        mesh.updateMorphTargets();

        if ( meshDef.weights !== undefined ) {

            for ( var i = 0, il = meshDef.weights.length; i < il; i ++ ) {

                mesh.morphTargetInfluences[ i ] = meshDef.weights[ i ];

            }

        }

        // .extras has user-defined data, so check that .extras.targetNames is an array.
        if ( meshDef.extras && Array.isArray( meshDef.extras.targetNames ) ) {

            var targetNames = meshDef.extras.targetNames;

            if ( mesh.morphTargetInfluences.length === targetNames.length ) {

                mesh.morphTargetDictionary = {};

                for ( var i = 0, il = targetNames.length; i < il; i ++ ) {

                    mesh.morphTargetDictionary[ targetNames[ i ] ] = i;

                }

            } else {

                console.warn( 'THREE.GLTFLoader: Invalid extras.targetNames length. Ignoring names.' );

            }

        }

    }

    function createPrimitiveKey( primitiveDef ) {

        var dracoExtension = primitiveDef.extensions && primitiveDef.extensions[ EXTENSIONS.KHR_DRACO_MESH_COMPRESSION ];
        var geometryKey;

        if ( dracoExtension ) {

            geometryKey = 'draco:' + dracoExtension.bufferView
                + ':' + dracoExtension.indices
                + ':' + createAttributesKey( dracoExtension.attributes );

        } else {

            geometryKey = primitiveDef.indices + ':' + createAttributesKey( primitiveDef.attributes ) + ':' + primitiveDef.mode;

        }

        return geometryKey;

    }

    function createAttributesKey( attributes ) {

        var attributesKey = '';

        var keys = Object.keys( attributes ).sort();

        for ( var i = 0, il = keys.length; i < il; i ++ ) {

            attributesKey += keys[ i ] + ':' + attributes[ keys[ i ] ] + ';';

        }

        return attributesKey;

    }

    function cloneBufferAttribute( attribute ) {

        if ( attribute.isInterleavedBufferAttribute ) {

            var count = attribute.count;
            var itemSize = attribute.itemSize;
            var array = attribute.array.slice( 0, count * itemSize );

            for ( var i = 0, j = 0; i < count; ++ i ) {

                array[ j ++ ] = attribute.getX( i );
                if ( itemSize >= 2 ) array[ j ++ ] = attribute.getY( i );
                if ( itemSize >= 3 ) array[ j ++ ] = attribute.getZ( i );
                if ( itemSize >= 4 ) array[ j ++ ] = attribute.getW( i );

            }

            return new THREE.BufferAttribute( array, itemSize, attribute.normalized );

        }

        return attribute.clone();

    }

    /* GLTF PARSER */

    function GLTFParser( json, extensions, options ) {

        this.json = json || {};
        this.extensions = extensions || {};
        this.options = options || {};

        // loader object cache
        this.cache = new GLTFRegistry();

        // BufferGeometry caching
        this.primitiveCache = {};

        this.textureLoader = new THREE.TextureLoader( this.options.manager );
        this.textureLoader.setCrossOrigin( this.options.crossOrigin );

        this.fileLoader = new THREE.FileLoader( this.options.manager );
        this.fileLoader.setResponseType( 'arraybuffer' );

        if ( this.options.crossOrigin === 'use-credentials' ) {

            this.fileLoader.setWithCredentials( true );

        }

    }

    GLTFParser.prototype.parse = function ( onLoad, onError ) {

        var parser = this;
        var json = this.json;
        var extensions = this.extensions;

        // Clear the loader cache
        this.cache.removeAll();

        // Mark the special nodes/meshes in json for efficient parse
        this.markDefs();

        Promise.all( [

            this.getDependencies( 'scene' ),
            this.getDependencies( 'animation' ),
            this.getDependencies( 'camera' ),

        ] ).then( function ( dependencies ) {

            var result = {
                scene: dependencies[ 0 ][ json.scene || 0 ],
                scenes: dependencies[ 0 ],
                animations: dependencies[ 1 ],
                cameras: dependencies[ 2 ],
                asset: json.asset,
                parser: parser,
                userData: {}
            };

            addUnknownExtensionsToUserData( extensions, result, json );

            assignExtrasToUserData( result, json );

            onLoad( result );

        } ).catch( onError );

    };

    /**
     * Marks the special nodes/meshes in json for efficient parse.
     */
    GLTFParser.prototype.markDefs = function () {

        var nodeDefs = this.json.nodes || [];
        var skinDefs = this.json.skins || [];
        var meshDefs = this.json.meshes || [];

        var meshReferences = {};
        var meshUses = {};

        // Nothing in the node definition indicates whether it is a Bone or an
        // Object3D. Use the skins' joint references to mark bones.
        for ( var skinIndex = 0, skinLength = skinDefs.length; skinIndex < skinLength; skinIndex ++ ) {

            var joints = skinDefs[ skinIndex ].joints;

            for ( var i = 0, il = joints.length; i < il; i ++ ) {

                nodeDefs[ joints[ i ] ].isBone = true;

            }

        }

        // Meshes can (and should) be reused by multiple nodes in a glTF asset. To
        // avoid having more than one THREE.Mesh with the same name, count
        // references and rename instances below.
        //
        // Example: CesiumMilkTruck sample model reuses "Wheel" meshes.
        for ( var nodeIndex = 0, nodeLength = nodeDefs.length; nodeIndex < nodeLength; nodeIndex ++ ) {

            var nodeDef = nodeDefs[ nodeIndex ];

            if ( nodeDef.mesh !== undefined ) {

                if ( meshReferences[ nodeDef.mesh ] === undefined ) {

                    meshReferences[ nodeDef.mesh ] = meshUses[ nodeDef.mesh ] = 0;

                }

                meshReferences[ nodeDef.mesh ] ++;

                // Nothing in the mesh definition indicates whether it is
                // a SkinnedMesh or Mesh. Use the node's mesh reference
                // to mark SkinnedMesh if node has skin.
                if ( nodeDef.skin !== undefined ) {

                    meshDefs[ nodeDef.mesh ].isSkinnedMesh = true;

                }

            }

        }

        this.json.meshReferences = meshReferences;
        this.json.meshUses = meshUses;

    };

    /**
     * Requests the specified dependency asynchronously, with caching.
     * @param {string} type
     * @param {number} index
     * @return {Promise<THREE.Object3D|THREE.Material|THREE.Texture|THREE.AnimationClip|ArrayBuffer|Object>}
     */
    GLTFParser.prototype.getDependency = function ( type, index ) {

        var cacheKey = type + ':' + index;
        var dependency = this.cache.get( cacheKey );

        if ( ! dependency ) {

            switch ( type ) {

                case 'scene':
                    dependency = this.loadScene( index );
                    break;

                case 'node':
                    dependency = this.loadNode( index );
                    break;

                case 'mesh':
                    dependency = this.loadMesh( index );
                    break;

                case 'accessor':
                    dependency = this.loadAccessor( index );
                    break;

                case 'bufferView':
                    dependency = this.loadBufferView( index );
                    break;

                case 'buffer':
                    dependency = this.loadBuffer( index );
                    break;

                case 'material':
                    dependency = this.loadMaterial( index );
                    break;

                case 'texture':
                    dependency = this.loadTexture( index );
                    break;

                case 'skin':
                    dependency = this.loadSkin( index );
                    break;

                case 'animation':
                    dependency = this.loadAnimation( index );
                    break;

                case 'camera':
                    dependency = this.loadCamera( index );
                    break;

                case 'light':
                    dependency = this.extensions[ EXTENSIONS.KHR_LIGHTS_PUNCTUAL ].loadLight( index );
                    break;

                default:
                    throw new Error( 'Unknown type: ' + type );

            }

            this.cache.add( cacheKey, dependency );

        }

        return dependency;

    };

    /**
     * Requests all dependencies of the specified type asynchronously, with caching.
     * @param {string} type
     * @return {Promise<Array<Object>>}
     */
    GLTFParser.prototype.getDependencies = function ( type ) {

        var dependencies = this.cache.get( type );

        if ( ! dependencies ) {

            var parser = this;
            var defs = this.json[ type + ( type === 'mesh' ? 'es' : 's' ) ] || [];

            dependencies = Promise.all( defs.map( function ( def, index ) {

                return parser.getDependency( type, index );

            } ) );

            this.cache.add( type, dependencies );

        }

        return dependencies;

    };

    /**
     * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#buffers-and-buffer-views
     * @param {number} bufferIndex
     * @return {Promise<ArrayBuffer>}
     */
    GLTFParser.prototype.loadBuffer = function ( bufferIndex ) {

        var bufferDef = this.json.buffers[ bufferIndex ];
        var loader = this.fileLoader;

        if ( bufferDef.type && bufferDef.type !== 'arraybuffer' ) {

            throw new Error( 'THREE.GLTFLoader: ' + bufferDef.type + ' buffer type is not supported.' );

        }

        // If present, GLB container is required to be the first buffer.
        if ( bufferDef.uri === undefined && bufferIndex === 0 ) {

            return Promise.resolve( this.extensions[ EXTENSIONS.KHR_BINARY_GLTF ].body );

        }

        var options = this.options;

        return new Promise( function ( resolve, reject ) {

            loader.load( resolveURL( bufferDef.uri, options.path ), resolve, undefined, function () {

                reject( new Error( 'THREE.GLTFLoader: Failed to load buffer "' + bufferDef.uri + '".' ) );

            } );

        } );

    };

    /**
     * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#buffers-and-buffer-views
     * @param {number} bufferViewIndex
     * @return {Promise<ArrayBuffer>}
     */
    GLTFParser.prototype.loadBufferView = function ( bufferViewIndex ) {

        var bufferViewDef = this.json.bufferViews[ bufferViewIndex ];

        return this.getDependency( 'buffer', bufferViewDef.buffer ).then( function ( buffer ) {

            var byteLength = bufferViewDef.byteLength || 0;
            var byteOffset = bufferViewDef.byteOffset || 0;
            return buffer.slice( byteOffset, byteOffset + byteLength );

        } );

    };

    /**
     * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#accessors
     * @param {number} accessorIndex
     * @return {Promise<THREE.BufferAttribute|THREE.InterleavedBufferAttribute>}
     */
    GLTFParser.prototype.loadAccessor = function ( accessorIndex ) {

        var parser = this;
        var json = this.json;

        var accessorDef = this.json.accessors[ accessorIndex ];

        if ( accessorDef.bufferView === undefined && accessorDef.sparse === undefined ) {

            // Ignore empty accessors, which may be used to declare runtime
            // information about attributes coming from another source (e.g. Draco
            // compression extension).
            return Promise.resolve( null );

        }

        var pendingBufferViews = [];

        if ( accessorDef.bufferView !== undefined ) {

            pendingBufferViews.push( this.getDependency( 'bufferView', accessorDef.bufferView ) );

        } else {

            pendingBufferViews.push( null );

        }

        if ( accessorDef.sparse !== undefined ) {

            pendingBufferViews.push( this.getDependency( 'bufferView', accessorDef.sparse.indices.bufferView ) );
            pendingBufferViews.push( this.getDependency( 'bufferView', accessorDef.sparse.values.bufferView ) );

        }

        return Promise.all( pendingBufferViews ).then( function ( bufferViews ) {

            var bufferView = bufferViews[ 0 ];

            var itemSize = WEBGL_TYPE_SIZES[ accessorDef.type ];
            var TypedArray = WEBGL_COMPONENT_TYPES[ accessorDef.componentType ];

            // For VEC3: itemSize is 3, elementBytes is 4, itemBytes is 12.
            var elementBytes = TypedArray.BYTES_PER_ELEMENT;
            var itemBytes = elementBytes * itemSize;
            var byteOffset = accessorDef.byteOffset || 0;
            var byteStride = accessorDef.bufferView !== undefined ? json.bufferViews[ accessorDef.bufferView ].byteStride : undefined;
            var normalized = accessorDef.normalized === true;
            var array, bufferAttribute;

            // The buffer is not interleaved if the stride is the item size in bytes.
            if ( byteStride && byteStride !== itemBytes ) {

                // Each "slice" of the buffer, as defined by 'count' elements of 'byteStride' bytes, gets its own InterleavedBuffer
                // This makes sure that IBA.count reflects accessor.count properly
                var ibSlice = Math.floor( byteOffset / byteStride );
                var ibCacheKey = 'InterleavedBuffer:' + accessorDef.bufferView + ':' + accessorDef.componentType + ':' + ibSlice + ':' + accessorDef.count;
                var ib = parser.cache.get( ibCacheKey );

                if ( ! ib ) {

                    array = new TypedArray( bufferView, ibSlice * byteStride, accessorDef.count * byteStride / elementBytes );

                    // Integer parameters to IB/IBA are in array elements, not bytes.
                    ib = new THREE.InterleavedBuffer( array, byteStride / elementBytes );

                    parser.cache.add( ibCacheKey, ib );

                }

                bufferAttribute = new THREE.InterleavedBufferAttribute( ib, itemSize, (byteOffset % byteStride) / elementBytes, normalized );

            } else {

                if ( bufferView === null ) {

                    array = new TypedArray( accessorDef.count * itemSize );

                } else {

                    array = new TypedArray( bufferView, byteOffset, accessorDef.count * itemSize );

                }

                bufferAttribute = new THREE.BufferAttribute( array, itemSize, normalized );

            }

            // https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#sparse-accessors
            if ( accessorDef.sparse !== undefined ) {

                var itemSizeIndices = WEBGL_TYPE_SIZES.SCALAR;
                var TypedArrayIndices = WEBGL_COMPONENT_TYPES[ accessorDef.sparse.indices.componentType ];

                var byteOffsetIndices = accessorDef.sparse.indices.byteOffset || 0;
                var byteOffsetValues = accessorDef.sparse.values.byteOffset || 0;

                var sparseIndices = new TypedArrayIndices( bufferViews[ 1 ], byteOffsetIndices, accessorDef.sparse.count * itemSizeIndices );
                var sparseValues = new TypedArray( bufferViews[ 2 ], byteOffsetValues, accessorDef.sparse.count * itemSize );

                if ( bufferView !== null ) {

                    // Avoid modifying the original ArrayBuffer, if the bufferView wasn't initialized with zeroes.
                    bufferAttribute.setArray( bufferAttribute.array.slice() );

                }

                for ( var i = 0, il = sparseIndices.length; i < il; i ++ ) {

                    var index = sparseIndices[ i ];

                    bufferAttribute.setX( index, sparseValues[ i * itemSize ] );
                    if ( itemSize >= 2 ) bufferAttribute.setY( index, sparseValues[ i * itemSize + 1 ] );
                    if ( itemSize >= 3 ) bufferAttribute.setZ( index, sparseValues[ i * itemSize + 2 ] );
                    if ( itemSize >= 4 ) bufferAttribute.setW( index, sparseValues[ i * itemSize + 3 ] );
                    if ( itemSize >= 5 ) throw new Error( 'THREE.GLTFLoader: Unsupported itemSize in sparse BufferAttribute.' );

                }

            }

            return bufferAttribute;

        } );

    };

    /**
     * Specification: https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#textures
     * @param {number} textureIndex
     * @return {Promise<THREE.Texture>}
     */
    GLTFParser.prototype.loadTexture = function ( textureIndex ) {

        var parser = this;
        var json = this.json;
        var options = this.options;
        var textureLoader = this.textureLoader;

        var URL = window.URL || window.webkitURL;

        var textureDef = json.textures[ textureIndex ];

        var textureExtensions = textureDef.extensions || {};

        var source;

        if ( textureExtensions[ EXTENSIONS.MSFT_TEXTURE_DDS ] ) {

            source = json.images[ textureExtensions[ EXTENSIONS.MSFT_TEXTURE_DDS ].source ];

    } else if ( textureExtensions[ EXTENSIONS.KHR_TEXTURE_BASISU ] ) {

      source = json.images[ textureExtensions[ EXTENSIONS.KHR_TEXTURE_BASISU ].source ];

        } else {

            source = json.images[ textureDef.source ];

        }

        var sourceURI = source.uri;
        var isObjectURL = false;

        if ( source.bufferView !== undefined ) {

            // Load binary image data from bufferView, if provided.

            sourceURI = parser.getDependency( 'bufferView', source.bufferView ).then( function ( bufferView ) {

                isObjectURL = true;
                var blob = new Blob( [ bufferView ], { type: source.mimeType } );
                sourceURI = URL.createObjectURL( blob );
                return sourceURI;

            } );

        }

        return Promise.resolve( sourceURI ).then( function ( sourceURI ) {

            // Load Texture resource.

            var loader = THREE.Loader.Handlers.get( sourceURI );

            if ( ! loader ) {

                loader = textureExtensions[ EXTENSIONS.MSFT_TEXTURE_DDS ]
                    ? parser.extensions[ EXTENSIONS.MSFT_TEXTURE_DDS ].ddsLoader
                    : textureLoader;

            }

            return new Promise( function ( resolve, reject ) {

                loader.load( resolveURL( sourceURI, options.path ), resolve, undefined, reject );

            } );

        } ).then( function ( texture ) {

            // Clean up resources and configure Texture.

            if ( isObjectURL === true ) {

                URL.revokeObjectURL( sourceURI );

            }

            texture.flipY = false;

            if ( textureDef.name !== undefined ) texture.name = textureDef.name;

            // Ignore unknown mime types, like DDS files.
            if ( source.mimeType in MIME_TYPE_FORMATS ) {

                texture.format = MIME_TYPE_FORMATS[ source.mimeType ];

            }

            var samplers = json.samplers || {};
            var sampler = samplers[ textureDef.sampler ] || {};

            texture.magFilter = WEBGL_FILTERS[ sampler.magFilter ] || THREE.LinearFilter;
            texture.minFilter = WEBGL_FILTERS[ sampler.minFilter ] || THREE.LinearMipmapLinearFilter;
            texture.wrapS = WEBGL_WRAPPINGS[ sampler.wrapS ] || THREE.RepeatWrapping;
            texture.wrapT = WEBGL_WRAPPINGS[ sampler.wrapT ] || THREE.RepeatWrapping;

            return texture;

        } );

    };

    /**
     * Asynchronously assigns a texture to the given material parameters.
     * @param {Object} materialParams
     * @param {string} mapName
     * @param {Object} mapDef
     * @return {Promise}
     */
    GLTFParser.prototype.assignTexture = function ( materialParams, mapName, mapDef ) {

        var parser = this;

        return this.getDependency( 'texture', mapDef.index ).then( function ( texture ) {

            if ( ! texture.isCompressedTexture ) {

                switch ( mapName ) {

                    case 'aoMap':
                    case 'emissiveMap':
                    case 'metalnessMap':
                    case 'normalMap':
                    case 'roughnessMap':
                        texture.format = THREE.RGBFormat;
                        break;

                }

            }

            if ( parser.extensions[ EXTENSIONS.KHR_TEXTURE_TRANSFORM ] ) {

                var transform = mapDef.extensions !== undefined ? mapDef.extensions[ EXTENSIONS.KHR_TEXTURE_TRANSFORM ] : undefined;

                if ( transform ) {

                    texture = parser.extensions[ EXTENSIONS.KHR_TEXTURE_TRANSFORM ].extendTexture( texture, transform );

                }

            }

            materialParams[ mapName ] = texture;

        } );

    };

    /**
     * Assigns final material to a Mesh, Line, or Points instance. The instance
     * already has a material (generated from the glTF material options alone)
     * but reuse of the same glTF material may require multiple threejs materials
     * to accomodate different primitive types, defines, etc. New materials will
     * be created if necessary, and reused from a cache.
     * @param  {THREE.Object3D} mesh Mesh, Line, or Points instance.
     */
    GLTFParser.prototype.assignFinalMaterial = function ( mesh ) {

        var geometry = mesh.geometry;
        var material = mesh.material;
        var extensions = this.extensions;

        var useVertexTangents = geometry.attributes.tangent !== undefined;
        var useVertexColors = geometry.attributes.color !== undefined;
        var useFlatShading = geometry.attributes.normal === undefined;
        var useSkinning = mesh.isSkinnedMesh === true;
        var useMorphTargets = Object.keys( geometry.morphAttributes ).length > 0;
        var useMorphNormals = useMorphTargets && geometry.morphAttributes.normal !== undefined;

        if ( mesh.isPoints ) {

            var cacheKey = 'PointsMaterial:' + material.uuid;

            var pointsMaterial = this.cache.get( cacheKey );

            if ( ! pointsMaterial ) {

                pointsMaterial = new THREE.PointsMaterial();
                THREE.Material.prototype.copy.call( pointsMaterial, material );
                pointsMaterial.color.copy( material.color );
                pointsMaterial.map = material.map;
                pointsMaterial.lights = false; // PointsMaterial doesn't support lights yet
                pointsMaterial.sizeAttenuation = false; // glTF spec says points should be 1px

                this.cache.add( cacheKey, pointsMaterial );

            }

            material = pointsMaterial;

        } else if ( mesh.isLine ) {

            var cacheKey = 'LineBasicMaterial:' + material.uuid;

            var lineMaterial = this.cache.get( cacheKey );

            if ( ! lineMaterial ) {

                lineMaterial = new THREE.LineBasicMaterial();
                THREE.Material.prototype.copy.call( lineMaterial, material );
                lineMaterial.color.copy( material.color );
                lineMaterial.lights = false; // LineBasicMaterial doesn't support lights yet

                this.cache.add( cacheKey, lineMaterial );

            }

            material = lineMaterial;

        }

        // Clone the material if it will be modified
        if ( useVertexTangents || useVertexColors || useFlatShading || useSkinning || useMorphTargets ) {

            var cacheKey = 'ClonedMaterial:' + material.uuid + ':';

            if ( material.isGLTFSpecularGlossinessMaterial ) cacheKey += 'specular-glossiness:';
            if ( useSkinning ) cacheKey += 'skinning:';
            if ( useVertexTangents ) cacheKey += 'vertex-tangents:';
            if ( useVertexColors ) cacheKey += 'vertex-colors:';
            if ( useFlatShading ) cacheKey += 'flat-shading:';
            if ( useMorphTargets ) cacheKey += 'morph-targets:';
            if ( useMorphNormals ) cacheKey += 'morph-normals:';

            var cachedMaterial = this.cache.get( cacheKey );

            if ( ! cachedMaterial ) {

                cachedMaterial = material.isGLTFSpecularGlossinessMaterial
                    ? extensions[ EXTENSIONS.KHR_MATERIALS_PBR_SPECULAR_GLOSSINESS ].cloneMaterial( material )
                    : material.clone();

                if ( useSkinning ) cachedMaterial.skinning = true;
                if ( useVertexTangents ) cachedMaterial.vertexTangents = true;
                if ( useVertexColors ) cachedMaterial.vertexColors = THREE.VertexColors;
                if ( useFlatShading ) cachedMaterial.flatShading = true;
                if ( useMorphTargets ) cachedMaterial.morphTargets = true;
                if ( useMorphNormals ) cachedMaterial.morphNormals = true;

                this.cache.add( cacheKey, cachedMaterial );

            }

            material = cachedMaterial;

        }

        // workarounds for mesh and geometry

        if ( material.aoMap && geometry.attributes.uv2 === undefined && geometry.attributes.uv !== undefined ) {

            console.log( 'THREE.GLTFLoader: Duplicating UVs to support aoMap.' );
            geometry.addAttribute( 'uv2', new THREE.BufferAttribute( geometry.attributes.uv.array, 2 ) );

        }

        if ( material.isGLTFSpecularGlossinessMaterial ) {

            // for GLTFSpecularGlossinessMaterial(ShaderMaterial) uniforms runtime update
            mesh.onBeforeRender = extensions[ EXTENSIONS.KHR_MATERIALS_PBR_SPECULAR_GLOSSINESS ].refreshUniforms;

        }

        mesh.material = material;

    };

    /**
     * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#materials
     * @param {number} materialIndex
     * @return {Promise<THREE.Material>}
     */
    GLTFParser.prototype.loadMaterial = function ( materialIndex ) {

        var parser = this;
        var json = this.json;
        var extensions = this.extensions;
        var materialDef = json.materials[ materialIndex ];

        var materialType;
        var materialParams = {};
        var materialExtensions = materialDef.extensions || {};

        var pending = [];

        if ( materialExtensions[ EXTENSIONS.KHR_MATERIALS_PBR_SPECULAR_GLOSSINESS ] ) {

            var sgExtension = extensions[ EXTENSIONS.KHR_MATERIALS_PBR_SPECULAR_GLOSSINESS ];
            materialType = sgExtension.getMaterialType();
            pending.push( sgExtension.extendParams( materialParams, materialDef, parser ) );

        } else if ( materialExtensions[ EXTENSIONS.KHR_MATERIALS_UNLIT ] ) {

            var kmuExtension = extensions[ EXTENSIONS.KHR_MATERIALS_UNLIT ];
            materialType = kmuExtension.getMaterialType();
            pending.push( kmuExtension.extendParams( materialParams, materialDef, parser ) );

        } else {

            // Specification:
            // https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#metallic-roughness-material

            materialType = THREE.MeshStandardMaterial;

            var metallicRoughness = materialDef.pbrMetallicRoughness || {};

            materialParams.color = new THREE.Color( 1.0, 1.0, 1.0 );
            materialParams.opacity = 1.0;

            if ( Array.isArray( metallicRoughness.baseColorFactor ) ) {

                var array = metallicRoughness.baseColorFactor;

                materialParams.color.fromArray( array );
                materialParams.opacity = array[ 3 ];

            }

            if ( metallicRoughness.baseColorTexture !== undefined ) {

                pending.push( parser.assignTexture( materialParams, 'map', metallicRoughness.baseColorTexture ) );

            }

            materialParams.metalness = metallicRoughness.metallicFactor !== undefined ? metallicRoughness.metallicFactor : 1.0;
            materialParams.roughness = metallicRoughness.roughnessFactor !== undefined ? metallicRoughness.roughnessFactor : 1.0;

            if ( metallicRoughness.metallicRoughnessTexture !== undefined ) {

                pending.push( parser.assignTexture( materialParams, 'metalnessMap', metallicRoughness.metallicRoughnessTexture ) );
                pending.push( parser.assignTexture( materialParams, 'roughnessMap', metallicRoughness.metallicRoughnessTexture ) );

            }

        }

        if ( materialDef.doubleSided === true ) {

            materialParams.side = THREE.DoubleSide;

        }

        var alphaMode = materialDef.alphaMode || ALPHA_MODES.OPAQUE;

        if ( alphaMode === ALPHA_MODES.BLEND ) {

            materialParams.transparent = true;

        } else {

            materialParams.transparent = false;

            if ( alphaMode === ALPHA_MODES.MASK ) {

                materialParams.alphaTest = materialDef.alphaCutoff !== undefined ? materialDef.alphaCutoff : 0.5;

            }

        }

        if ( materialDef.normalTexture !== undefined && materialType !== THREE.MeshBasicMaterial ) {

            pending.push( parser.assignTexture( materialParams, 'normalMap', materialDef.normalTexture ) );

            materialParams.normalScale = new THREE.Vector2( 1, 1 );

            if ( materialDef.normalTexture.scale !== undefined ) {

                materialParams.normalScale.set( materialDef.normalTexture.scale, materialDef.normalTexture.scale );

            }

        }

        if ( materialDef.occlusionTexture !== undefined && materialType !== THREE.MeshBasicMaterial ) {

            pending.push( parser.assignTexture( materialParams, 'aoMap', materialDef.occlusionTexture ) );

            if ( materialDef.occlusionTexture.strength !== undefined ) {

                materialParams.aoMapIntensity = materialDef.occlusionTexture.strength;

            }

        }

        if ( materialDef.emissiveFactor !== undefined && materialType !== THREE.MeshBasicMaterial ) {

            materialParams.emissive = new THREE.Color().fromArray( materialDef.emissiveFactor );

        }

        if ( materialDef.emissiveTexture !== undefined && materialType !== THREE.MeshBasicMaterial ) {

            pending.push( parser.assignTexture( materialParams, 'emissiveMap', materialDef.emissiveTexture ) );

        }

        return Promise.all( pending ).then( function () {

            var material;

            if ( materialType === THREE.ShaderMaterial ) {

                material = extensions[ EXTENSIONS.KHR_MATERIALS_PBR_SPECULAR_GLOSSINESS ].createMaterial( materialParams );

            } else {

                material = new materialType( materialParams );

            }

            if ( materialDef.name !== undefined ) material.name = materialDef.name;

            // baseColorTexture, emissiveTexture, and specularGlossinessTexture use sRGB encoding.
            if ( material.map ) material.map.encoding = THREE.sRGBEncoding;
            if ( material.emissiveMap ) material.emissiveMap.encoding = THREE.sRGBEncoding;
            if ( material.specularMap ) material.specularMap.encoding = THREE.sRGBEncoding;

            assignExtrasToUserData( material, materialDef );

            if ( materialDef.extensions ) addUnknownExtensionsToUserData( extensions, material, materialDef );

            return material;

        } );

    };

    /**
     * @param {THREE.BufferGeometry} geometry
     * @param {GLTF.Primitive} primitiveDef
     * @param {GLTFParser} parser
     * @return {Promise<THREE.BufferGeometry>}
     */
    function addPrimitiveAttributes( geometry, primitiveDef, parser ) {

        var attributes = primitiveDef.attributes;

        var pending = [];

        function assignAttributeAccessor( accessorIndex, attributeName ) {

            return parser.getDependency( 'accessor', accessorIndex )
                .then( function ( accessor ) {

                    geometry.addAttribute( attributeName, accessor );

                } );

        }

        for ( var gltfAttributeName in attributes ) {

            var threeAttributeName = ATTRIBUTES[ gltfAttributeName ] || gltfAttributeName.toLowerCase();

            // Skip attributes already provided by e.g. Draco extension.
            if ( threeAttributeName in geometry.attributes ) continue;

            pending.push( assignAttributeAccessor( attributes[ gltfAttributeName ], threeAttributeName ) );

        }

        if ( primitiveDef.indices !== undefined && ! geometry.index ) {

            var accessor = parser.getDependency( 'accessor', primitiveDef.indices ).then( function ( accessor ) {

                geometry.setIndex( accessor );

            } );

            pending.push( accessor );

        }

        assignExtrasToUserData( geometry, primitiveDef );

        return Promise.all( pending ).then( function () {

            return primitiveDef.targets !== undefined
                ? addMorphTargets( geometry, primitiveDef.targets, parser )
                : geometry;

        } );

    }

    /**
     * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#geometry
     *
     * Creates BufferGeometries from primitives.
     *
     * @param {Array<GLTF.Primitive>} primitives
     * @return {Promise<Array<THREE.BufferGeometry>>}
     */
    GLTFParser.prototype.loadGeometries = function ( primitives ) {

        var parser = this;
        var extensions = this.extensions;
        var cache = this.primitiveCache;

        function createDracoPrimitive( primitive ) {

            return extensions[ EXTENSIONS.KHR_DRACO_MESH_COMPRESSION ]
                .decodePrimitive( primitive, parser )
                .then( function ( geometry ) {

                    return addPrimitiveAttributes( geometry, primitive, parser );

                } );

        }

        var pending = [];

        for ( var i = 0, il = primitives.length; i < il; i ++ ) {

            var primitive = primitives[ i ];
            var cacheKey = createPrimitiveKey( primitive );

            // See if we've already created this geometry
            var cached = cache[ cacheKey ];

            if ( cached ) {

                // Use the cached geometry if it exists
                pending.push( cached.promise );

            } else {

                var geometryPromise;

                if ( primitive.extensions && primitive.extensions[ EXTENSIONS.KHR_DRACO_MESH_COMPRESSION ] ) {

                    // Use DRACO geometry if available
                    geometryPromise = createDracoPrimitive( primitive );

                } else {

                    // Otherwise create a new geometry
                    geometryPromise = addPrimitiveAttributes( new THREE.BufferGeometry(), primitive, parser );

                }

                // Cache this geometry
                cache[ cacheKey ] = { primitive: primitive, promise: geometryPromise };

                pending.push( geometryPromise );

            }

        }

        return Promise.all( pending );

    };

    /**
     * Specification: https://github.com/KhronosGroup/glTF/blob/master/specification/2.0/README.md#meshes
     * @param {number} meshIndex
     * @return {Promise<THREE.Group|THREE.Mesh|THREE.SkinnedMesh>}
     */
    GLTFParser.prototype.loadMesh = function ( meshIndex ) {

        var parser = this;
        var json = this.json;

        var meshDef = json.meshes[ meshIndex ];
        var primitives = meshDef.primitives;

        var pending = [];

        for ( var i = 0, il = primitives.length; i < il; i ++ ) {

            var material = primitives[ i ].material === undefined
                ? createDefaultMaterial()
                : this.getDependency( 'material', primitives[ i ].material );

            pending.push( material );

        }

        return Promise.all( pending ).then( function ( originalMaterials ) {

            return parser.loadGeometries( primitives ).then( function ( geometries ) {

                var meshes = [];

                for ( var i = 0, il = geometries.length; i < il; i ++ ) {

                    var geometry = geometries[ i ];
                    var primitive = primitives[ i ];

                    // 1. create Mesh

                    var mesh;

                    var material = originalMaterials[ i ];

                    if ( primitive.mode === WEBGL_CONSTANTS.TRIANGLES ||
                        primitive.mode === WEBGL_CONSTANTS.TRIANGLE_STRIP ||
                        primitive.mode === WEBGL_CONSTANTS.TRIANGLE_FAN ||
                        primitive.mode === undefined ) {

                        // .isSkinnedMesh isn't in glTF spec. See .markDefs()
                        mesh = meshDef.isSkinnedMesh === true
                            ? new THREE.SkinnedMesh( geometry, material )
                            : new THREE.Mesh( geometry, material );

                        if ( mesh.isSkinnedMesh === true && ! mesh.geometry.attributes.skinWeight.normalized ) {

                            // we normalize floating point skin weight array to fix malformed assets (see #15319)
                            // it's important to skip this for non-float32 data since normalizeSkinWeights assumes non-normalized inputs
                            mesh.normalizeSkinWeights();

                        }

                        if ( primitive.mode === WEBGL_CONSTANTS.TRIANGLE_STRIP ) {

                            mesh.drawMode = THREE.TriangleStripDrawMode;

                        } else if ( primitive.mode === WEBGL_CONSTANTS.TRIANGLE_FAN ) {

                            mesh.drawMode = THREE.TriangleFanDrawMode;

                        }

                    } else if ( primitive.mode === WEBGL_CONSTANTS.LINES ) {

                        mesh = new THREE.LineSegments( geometry, material );

                    } else if ( primitive.mode === WEBGL_CONSTANTS.LINE_STRIP ) {

                        mesh = new THREE.Line( geometry, material );

                    } else if ( primitive.mode === WEBGL_CONSTANTS.LINE_LOOP ) {

                        mesh = new THREE.LineLoop( geometry, material );

                    } else if ( primitive.mode === WEBGL_CONSTANTS.POINTS ) {

                        mesh = new THREE.Points( geometry, material );

                    } else {

                        throw new Error( 'THREE.GLTFLoader: Primitive mode unsupported: ' + primitive.mode );

                    }

                    if ( Object.keys( mesh.geometry.morphAttributes ).length > 0 ) {

                        updateMorphTargets( mesh, meshDef );

                    }

                    mesh.name = meshDef.name || ( 'mesh_' + meshIndex );

                    if ( geometries.length > 1 ) mesh.name += '_' + i;

                    assignExtrasToUserData( mesh, meshDef );

                    parser.assignFinalMaterial( mesh );

                    meshes.push( mesh );

                }

                if ( meshes.length === 1 ) {

                    return meshes[ 0 ];

                }

                var group = new THREE.Group();

                for ( var i = 0, il = meshes.length; i < il; i ++ ) {

                    group.add( meshes[ i ] );

                }

                return group;

            } );

        } );

    };

    /**
     * Specification: https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#cameras
     * @param {number} cameraIndex
     * @return {Promise<THREE.Camera>}
     */
    GLTFParser.prototype.loadCamera = function ( cameraIndex ) {

        var camera;
        var cameraDef = this.json.cameras[ cameraIndex ];
        var params = cameraDef[ cameraDef.type ];

        if ( ! params ) {

            console.warn( 'THREE.GLTFLoader: Missing camera parameters.' );
            return;

        }

        if ( cameraDef.type === 'perspective' ) {

            camera = new THREE.PerspectiveCamera( THREE.Math.radToDeg( params.yfov ), params.aspectRatio || 1, params.znear || 1, params.zfar || 2e6 );

        } else if ( cameraDef.type === 'orthographic' ) {

            camera = new THREE.OrthographicCamera( params.xmag / - 2, params.xmag / 2, params.ymag / 2, params.ymag / - 2, params.znear, params.zfar );

        }

        if ( cameraDef.name !== undefined ) camera.name = cameraDef.name;

        assignExtrasToUserData( camera, cameraDef );

        return Promise.resolve( camera );

    };

    /**
     * Specification: https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#skins
     * @param {number} skinIndex
     * @return {Promise<Object>}
     */
    GLTFParser.prototype.loadSkin = function ( skinIndex ) {

        var skinDef = this.json.skins[ skinIndex ];

        var skinEntry = { joints: skinDef.joints };

        if ( skinDef.inverseBindMatrices === undefined ) {

            return Promise.resolve( skinEntry );

        }

        return this.getDependency( 'accessor', skinDef.inverseBindMatrices ).then( function ( accessor ) {

            skinEntry.inverseBindMatrices = accessor;

            return skinEntry;

        } );

    };

    /**
     * Specification: https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#animations
     * @param {number} animationIndex
     * @return {Promise<THREE.AnimationClip>}
     */
    GLTFParser.prototype.loadAnimation = function ( animationIndex ) {

        var json = this.json;

        var animationDef = json.animations[ animationIndex ];

        var pendingNodes = [];
        var pendingInputAccessors = [];
        var pendingOutputAccessors = [];
        var pendingSamplers = [];
        var pendingTargets = [];

        for ( var i = 0, il = animationDef.channels.length; i < il; i ++ ) {

            var channel = animationDef.channels[ i ];
            var sampler = animationDef.samplers[ channel.sampler ];
            var target = channel.target;
            var name = target.node !== undefined ? target.node : target.id; // NOTE: target.id is deprecated.
            var input = animationDef.parameters !== undefined ? animationDef.parameters[ sampler.input ] : sampler.input;
            var output = animationDef.parameters !== undefined ? animationDef.parameters[ sampler.output ] : sampler.output;

            pendingNodes.push( this.getDependency( 'node', name ) );
            pendingInputAccessors.push( this.getDependency( 'accessor', input ) );
            pendingOutputAccessors.push( this.getDependency( 'accessor', output ) );
            pendingSamplers.push( sampler );
            pendingTargets.push( target );

        }

        return Promise.all( [

            Promise.all( pendingNodes ),
            Promise.all( pendingInputAccessors ),
            Promise.all( pendingOutputAccessors ),
            Promise.all( pendingSamplers ),
            Promise.all( pendingTargets )

        ] ).then( function ( dependencies ) {

            var nodes = dependencies[ 0 ];
            var inputAccessors = dependencies[ 1 ];
            var outputAccessors = dependencies[ 2 ];
            var samplers = dependencies[ 3 ];
            var targets = dependencies[ 4 ];

            var tracks = [];

            for ( var i = 0, il = nodes.length; i < il; i ++ ) {

                var node = nodes[ i ];
                var inputAccessor = inputAccessors[ i ];
                var outputAccessor = outputAccessors[ i ];
                var sampler = samplers[ i ];
                var target = targets[ i ];

                if ( node === undefined ) continue;

                node.updateMatrix();
                node.matrixAutoUpdate = true;

                var TypedKeyframeTrack;

                switch ( PATH_PROPERTIES[ target.path ] ) {

                    case PATH_PROPERTIES.weights:

                        TypedKeyframeTrack = THREE.NumberKeyframeTrack;
                        break;

                    case PATH_PROPERTIES.rotation:

                        TypedKeyframeTrack = THREE.QuaternionKeyframeTrack;
                        break;

                    case PATH_PROPERTIES.position:
                    case PATH_PROPERTIES.scale:
                    default:

                        TypedKeyframeTrack = THREE.VectorKeyframeTrack;
                        break;

                }

                var targetName = node.name ? node.name : node.uuid;

                var interpolation = sampler.interpolation !== undefined ? INTERPOLATION[ sampler.interpolation ] : THREE.InterpolateLinear;

                var targetNames = [];

                if ( PATH_PROPERTIES[ target.path ] === PATH_PROPERTIES.weights ) {

                    // Node may be a THREE.Group (glTF mesh with several primitives) or a THREE.Mesh.
                    node.traverse( function ( object ) {

                        if ( object.isMesh === true && object.morphTargetInfluences ) {

                            targetNames.push( object.name ? object.name : object.uuid );

                        }

                    } );

                } else {

                    targetNames.push( targetName );

                }

                var outputArray = outputAccessor.array;

                if ( outputAccessor.normalized ) {

                    var scale;

                    if ( outputArray.constructor === Int8Array ) {

                        scale = 1 / 127;

                    } else if ( outputArray.constructor === Uint8Array ) {

                        scale = 1 / 255;

                    } else if ( outputArray.constructor == Int16Array ) {

                        scale = 1 / 32767;

                    } else if ( outputArray.constructor === Uint16Array ) {

                        scale = 1 / 65535;

                    } else {

                        throw new Error( 'THREE.GLTFLoader: Unsupported output accessor component type.' );

                    }

                    var scaled = new Float32Array( outputArray.length );

                    for ( var j = 0, jl = outputArray.length; j < jl; j ++ ) {

                        scaled[ j ] = outputArray[ j ] * scale;

                    }

                    outputArray = scaled;

                }

                for ( var j = 0, jl = targetNames.length; j < jl; j ++ ) {

                    var track = new TypedKeyframeTrack(
                        targetNames[ j ] + '.' + PATH_PROPERTIES[ target.path ],
                        inputAccessor.array,
                        outputArray,
                        interpolation
                    );

                    // Override interpolation with custom factory method.
                    if ( sampler.interpolation === 'CUBICSPLINE' ) {

                        track.createInterpolant = function InterpolantFactoryMethodGLTFCubicSpline( result ) {

                            // A CUBICSPLINE keyframe in glTF has three output values for each input value,
                            // representing inTangent, splineVertex, and outTangent. As a result, track.getValueSize()
                            // must be divided by three to get the interpolant's sampleSize argument.

                            return new GLTFCubicSplineInterpolant( this.times, this.values, this.getValueSize() / 3, result );

                        };

                        // Mark as CUBICSPLINE. `track.getInterpolation()` doesn't support custom interpolants.
                        track.createInterpolant.isInterpolantFactoryMethodGLTFCubicSpline = true;

                    }

                    tracks.push( track );

                }

            }

            var name = animationDef.name !== undefined ? animationDef.name : 'animation_' + animationIndex;

            return new THREE.AnimationClip( name, undefined, tracks );

        } );

    };

    /**
     * Specification: https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#nodes-and-hierarchy
     * @param {number} nodeIndex
     * @return {Promise<THREE.Object3D>}
     */
    GLTFParser.prototype.loadNode = function ( nodeIndex ) {

        var json = this.json;
        var extensions = this.extensions;
        var parser = this;

        var meshReferences = json.meshReferences;
        var meshUses = json.meshUses;

        var nodeDef = json.nodes[ nodeIndex ];

        return ( function () {

            var pending = [];

            if ( nodeDef.mesh !== undefined ) {

                pending.push( parser.getDependency( 'mesh', nodeDef.mesh ).then( function ( mesh ) {

                    var node;

                    if ( meshReferences[ nodeDef.mesh ] > 1 ) {

                        var instanceNum = meshUses[ nodeDef.mesh ] ++;

                        node = mesh.clone();
                        node.name += '_instance_' + instanceNum;

                        // onBeforeRender copy for Specular-Glossiness
                        node.onBeforeRender = mesh.onBeforeRender;

                        for ( var i = 0, il = node.children.length; i < il; i ++ ) {

                            node.children[ i ].name += '_instance_' + instanceNum;
                            node.children[ i ].onBeforeRender = mesh.children[ i ].onBeforeRender;

                        }

                    } else {

                        node = mesh;

                    }

                    // if weights are provided on the node, override weights on the mesh.
                    if ( nodeDef.weights !== undefined ) {

                        node.traverse( function ( o ) {

                            if ( ! o.isMesh ) return;

                            for ( var i = 0, il = nodeDef.weights.length; i < il; i ++ ) {

                                o.morphTargetInfluences[ i ] = nodeDef.weights[ i ];

                            }

                        } );

                    }

                    return node;

                } ) );

            }

            if ( nodeDef.camera !== undefined ) {

                pending.push( parser.getDependency( 'camera', nodeDef.camera ) );

            }

            if ( nodeDef.extensions
                && nodeDef.extensions[ EXTENSIONS.KHR_LIGHTS_PUNCTUAL ]
                && nodeDef.extensions[ EXTENSIONS.KHR_LIGHTS_PUNCTUAL ].light !== undefined ) {

                pending.push( parser.getDependency( 'light', nodeDef.extensions[ EXTENSIONS.KHR_LIGHTS_PUNCTUAL ].light ) );

            }

            return Promise.all( pending );

        }() ).then( function ( objects ) {

            var node;

            // .isBone isn't in glTF spec. See .markDefs
            if ( nodeDef.isBone === true ) {

                node = new THREE.Bone();

            } else if ( objects.length > 1 ) {

                node = new THREE.Group();

            } else if ( objects.length === 1 ) {

                node = objects[ 0 ];

            } else {

                node = new THREE.Object3D();

            }

            if ( node !== objects[ 0 ] ) {

                for ( var i = 0, il = objects.length; i < il; i ++ ) {

                    node.add( objects[ i ] );

                }

            }

            if ( nodeDef.name !== undefined ) {

                node.userData.name = nodeDef.name;
                node.name = THREE.PropertyBinding.sanitizeNodeName( nodeDef.name );

            }

            assignExtrasToUserData( node, nodeDef );

            if ( nodeDef.extensions ) addUnknownExtensionsToUserData( extensions, node, nodeDef );

            if ( nodeDef.matrix !== undefined ) {

                var matrix = new THREE.Matrix4();
                matrix.fromArray( nodeDef.matrix );
                node.applyMatrix( matrix );

            } else {

                if ( nodeDef.translation !== undefined ) {

                    node.position.fromArray( nodeDef.translation );

                }

                if ( nodeDef.rotation !== undefined ) {

                    node.quaternion.fromArray( nodeDef.rotation );

                }

                if ( nodeDef.scale !== undefined ) {

                    node.scale.fromArray( nodeDef.scale );

                }

            }

            return node;

        } );

    };

    /**
     * Specification: https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#scenes
     * @param {number} sceneIndex
     * @return {Promise<THREE.Scene>}
     */
    GLTFParser.prototype.loadScene = function () {

        // scene node hierachy builder

        function buildNodeHierachy( nodeId, parentObject, json, parser ) {

            var nodeDef = json.nodes[ nodeId ];

            return parser.getDependency( 'node', nodeId ).then( function ( node ) {

                if ( nodeDef.skin === undefined ) return node;

                // build skeleton here as well

                var skinEntry;

                return parser.getDependency( 'skin', nodeDef.skin ).then( function ( skin ) {

                    skinEntry = skin;

                    var pendingJoints = [];

                    for ( var i = 0, il = skinEntry.joints.length; i < il; i ++ ) {

                        pendingJoints.push( parser.getDependency( 'node', skinEntry.joints[ i ] ) );

                    }

                    return Promise.all( pendingJoints );

                } ).then( function ( jointNodes ) {

                    node.traverse( function ( mesh ) {

                        if ( ! mesh.isMesh ) return;

                        var bones = [];
                        var boneInverses = [];

                        for ( var j = 0, jl = jointNodes.length; j < jl; j ++ ) {

                            var jointNode = jointNodes[ j ];

                            if ( jointNode ) {

                                bones.push( jointNode );

                                var mat = new THREE.Matrix4();

                                if ( skinEntry.inverseBindMatrices !== undefined ) {

                                    mat.fromArray( skinEntry.inverseBindMatrices.array, j * 16 );

                                }

                                boneInverses.push( mat );

                            } else {

                                console.warn( 'THREE.GLTFLoader: Joint "%s" could not be found.', skinEntry.joints[ j ] );

                            }

                        }

                        mesh.bind( new THREE.Skeleton( bones, boneInverses ), mesh.matrixWorld );

                    } );

                    return node;

                } );

            } ).then( function ( node ) {

                // build node hierachy

                parentObject.add( node );

                var pending = [];

                if ( nodeDef.children ) {

                    var children = nodeDef.children;

                    for ( var i = 0, il = children.length; i < il; i ++ ) {

                        var child = children[ i ];
                        pending.push( buildNodeHierachy( child, node, json, parser ) );

                    }

                }

                return Promise.all( pending );

            } );

        }

        return function loadScene( sceneIndex ) {

            var json = this.json;
            var extensions = this.extensions;
            var sceneDef = this.json.scenes[ sceneIndex ];
            var parser = this;

            var scene = new THREE.Scene();
            if ( sceneDef.name !== undefined ) scene.name = sceneDef.name;

            assignExtrasToUserData( scene, sceneDef );

            if ( sceneDef.extensions ) addUnknownExtensionsToUserData( extensions, scene, sceneDef );

            var nodeIds = sceneDef.nodes || [];

            var pending = [];

            for ( var i = 0, il = nodeIds.length; i < il; i ++ ) {

                pending.push( buildNodeHierachy( nodeIds[ i ], scene, json, parser ) );

            }

            return Promise.all( pending ).then( function () {

                return scene;

            } );

        };

    }();

    return GLTFLoader;

} )();
